Vulnerable plaques are lipid filled cavities that form within the wall of an artery. These plaques, when ruptured, can cause massive clotting in the artery. The resultant clot can interfere with blood flow to the brain, resulting in a stroke, or with blood flow to the coronary arteries, resulting in a heart attack.
To locate vulnerable plaques, one inserts a catheter through the lumen of the artery. The catheter includes a delivery fiber for illuminating a spot on the arterial wall and a collection fiber for collecting scattered light that results from that illumination. The delivery fiber and the collection fiber form distinct optical channels within the catheter.
Light propagating on the delivery fiber travels axially, along the axis of the catheter. A delivery mirror intercepts this light and directs it radially outward so that it illuminates an illumination spot on the arterial wall. A collection mirror intercepts light scattered from inside the arterial wall and directs it axially, into the collection fiber.
The collection mirror is disposed or oriented such that the scattered light is received from a collection zone that is separate from the illumination zone. This minimizes glare resulting from specular reflection from the arterial wall.